Dry metallurgical process for extracting lead from its sulphide or oxidized ore



SPf- 2 1953 A. BERTRAND 2,850,375

:my METALLURGICAL PRocEss RoR EXTRACTING LEAD FROM :Ts suLPHIDE oRoxrnrzED ORE Filtd Aug. v24K. 1953 2 Sheets-Shget 1 Sept 2, 1955 A.BERTRAND 2,850,375

DRY METALLURGICAL PROCESS FOR EXTRACTING LEAD FROM 4 ITS SULPHIDE OROXIDIZED ORE Filed Aug. 24. 1953 2 Sheets-Sheet 2 nited States arentatented Sept. 2, 1953 d. t n

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DRY METALLURGICAL PROCESS FR EXTRACT- ING LEAD FROM ITS SULPHIDE ROXDIZED ORE Andr Eertrand, Casablanca, Morocco Application August 24,1953, Serial No. 376,131 Claims priority, application Morocco August 25,1952 Claims. (Cl. 75-77) This invention relates to the metallurgy ofheavy metals and it has for its object improvements to processes of thedry metallurgy of heavy metals such as lead, antimony, tin, copper andzinc. More particularly, it concerns the obtaining of these metals inthe metallic state, starting from their sulphide or oxidized ores.

In the case of sulphide ores such as blende or stibnite, the liberationreaction of the metal may take place by oxidation, byoxidation-reduction or by precipitation. The last mentioned method maybe accomplished by causing the ore to react on metallic iron so as toobtain the well known reaction:

MS-l-FeeM-l-FeS in which M represents the heavy metal under consideraotion.

This process has never received any important industrial development andhas always been abandoned owing to the bad yields obtained. The reactionsuffers from the serious drawback of being limited by the formation ofan eutectic between the iron sulphide formed and the sulphide of thetreated ore, this eutectic forming a matte which carries away the metalsought in the dross and limits the quantity that is extracted.

ln addition, in the case of both the sulphide and the oxidised ore, theliberated metal has always been dithcult to separate fromvthe slag owingto the lack of fluidity of the latter. Various additions have alreadybeen proposed intended to lower the melting point of the slag and torender the latter more uid, but none of these known processes hasovercome the dihculties constituted by the formation of the matte ofmixed sulphide.

The present invention has for its object to provide a new processtending to overcome these diiculties by permitting simultaneously toobtain a slag which is extremely fuid and to dissociate the eutectic ofmixed sulphide as it is formed. ln this manner, a practicallyquantitative yield of the metal and an easy separation of the latter romthe slag are obtained.

To this end, the invention is based on the verification that, for a verynarrow range of relative proportions of lime, silica and alumina, theslag which is formed has the surprising property of causing thedissociation of the eutectic of mixed sulphide.

lt so happens that, in this same range of proportions, the melting pointof the slag is particularly low and corresponds to an eutectic valley onthe ternary diagram. lt is therefore possible to define the compositionof the slag causing this decomposition of the eutectics of mixedsulphides by the zone situated in the eutectic valley of the ternarydiagram comprised between SiO2, CaO and 2Si02, M203, CaO.

The ternary diagram which has just been mentioned is well known tometallurgists. lt defines the 'temperature of fusion of each possiblecomposition SiOg. A1203 and CaO. ln practice, in the treatment of anatural ore,

ed other constituents are met which may inuence the temperature offusion of the slag. However, the essential constituents of this slag arelime, silica and alumina, and the process according to the inventionconsist in the application of a discovery directed to the considerationof a property which is characteristic of the compoundslime-silica-aiumina only.

Prom the above, it will be understood that, in the case of the sulphideores, the invention consists in causing the formation of the slagreferred to. However, it will be moreover notice that, this slag beingthe most fluid that it is possible to obtain, it ensures a much moreeasy separation of the extracted metal as well in the case of the metalobtained from its sulphide as in the case of a metal obtained from anoxidised ore, for example by reduction of such an ore by means ofcarbon.

The process according to the invention, therefore, consists in enhancingthe separation of the metal as it is formed by adjusting for thispurpose the composition of the slag with respect to the initial contentof the gangue in lime, silica and alumina, as well as to the compositionof the ashes of the fuel used, so that the final composition of thisslag with respect to lime, silica and alumina is represented by a pointsituated in the eutectic valley of the ternary diagram comprised betweenthe combinations Si02, CaO and 2SiO2 A1203, CaO.

Referring now to the ternary diagram as represented in Fig. l of theappended drawing, it will be seen that, by marldng on the three sides ofthe equilateral triangle ABC increasing percentages of alumina, silicaand lime, each point in this triangle corresponding to a particularcombination having given proportions of these three con sti'tuents andthe melting point of this compound being indicated, there exists on theside AC a point M corresponding to the compound Si02, CaO and, in theinside of the triangle, a point N corresponding to the compound 2Si02,A1203, CaO. The melting points of these two compounds, respectively, arehigher than l5l0 C. If however the region between M and N is considered,isothermal curves are observed in that region Corresp-onfing to lowertemperatures, namely 1400 and 1300 C. There are in fact two 1300 C.isothermals, between which there happens to be a eutectic Valley PQ,itself limited by two other eutectic curves and the melting point ofwhich is comprised between 1165 C. (for P) and 1265 C. (for Q). Theinvention consists in the discovery that, if the composition of the slagis so adjusted that the point representing it is situated in the shadedzone of the ternary diagram surrounding the valley PQ, and moreparticularly limited by the 1390 C. isothermals, the dissociation of theeutec'tic PbS-Fe, for example, is brought about, while an extremely duidslag is obtained, which ensures an easy separation of the metalextracted.

According to an important characteristic feature of the invention, theprocess previously mentioned must therefore be limited to the adjustmentof the composition of the slag to the zone aforesaid, namely, thatlimited by the 13GG C. isotherme.

in carrying out the invention in practice, it is only necessary toperform an analysis of the gangue of the ore and of the ashes of thefuel used. With the result of this analysis, together with thepercentage of gangue of the ore and the quantity of fuel added for thetreat-l ment of this ore, the nature and the quantity of the componentsto be introduced in order to bring the composition of the slag in thezone aforesaid may be deduced therefrom. This may be obtained either bycalculation or by a very simple graphical construction, which will benow explained with reference to the following example.

Example Percent Pb 68 Si02 8 A1203 2 CaO 1 In order to maintain areducing atmosphere, of coke dust is added to the ore, having thefollowing com- The quantity of metallic iron to be added as a functionof the percentage of lead existing in the form of PbS in the ore iscalculated from the equation This quantity of iron is equal to 0.27times the quantity of lead. It does not in any Way alter the calculationof the slags and in what follows only the quantity of silica, lime andalumina used are taken into consideration.

To this end, the percentages of raw materials will be given in thefollowing table, taking into account the fact that the lead ore contains11% gangue, the fuel contains 14% gangue and the lime contains 93% ofproducts with which the diagram is concerned. Bringing these quantitiesto 100%, the three points of the diagram corresponding to the threegangue compositions are ascertained.

In order to find the composition of the slag obtained without any otheraddition than the ore and the fuel, a graphical construction,represented in Fig. 2, may be used. The points R, S and T having beenplotted on the ternary diagram, from the points R and S parallel vectorsRr and Ss are drawn, having respectively a length inversely proportionalto the mass of the fuel gangue and to the mass or the ore gangue. Byjoining rs, the point w is obtained, which represents the composition ofthe slag as a function of the quantities of the compounds having thecompositions represented by the points R and S. This point w is situatedoutside the zone surrounding the valley PQ and the invention consists inadding lime (having the composition represented by T) in such quantitythat the resulting slag will have a composition represented by a pointsituated in that zone. To do this, a vector Tt proportional to the totalof the quantities of ore and fuel is drawn and the line T w is drawn,in-

tersecting PQ at Q. The points t and Sl are then joined and the line t9is produced till it meets at w a line parallel to Tt drawn through w.The value of the vector ww' gives the proportion of lime having thecomposition given above which it is necessary to add to obtain thedesired slag.

vIy Naturally, the same result could be obtained by calculation, andthis can be performed in a very simple manner: measuring the lengths ofthe lines Qw and SlT enables the weight x of lime to be added to befound. For the point Q representing the nal slag must satisfy theequation (Weight of ore+weight of fuel) lw=TSl x y whence the value of xis deduced.

It will be noticed -that neither the construction nor the calculationintroduces the fact that the ore is a sulphide or an oxide or is of anyother nature, so that the present process is applicable to any ore, itsutility being greater in the case of a sulphide ore, however, since notthe fluidity of the slag enables a better separation of the metal to beobtained, but also its nature ensures the quantitative yield of thereaction by dissociating the mixed sulphide formed.

The processdescribed above is preferably applicable Vto lead, antimonyand tin. It may also be used, but not so advantageously, in connectionwith copper and zinc ores.

Should the slag not yet be suiciently fluid at the very low temperturessuch as 1100 to 1280 C., 1 or 2% of fluor-spar or sodium carbonate maybe added.

What I claim is:

1. In a dry metallurgical process for the extraction of lead from itsore; the step of adjusting the composition of the slag formed at the endof the process by adding 'te the ore and fuel a compound of lime, silicaand alumina the proportions of which are so related with rrespect to theinitial content of the ore gangue and of the content of lime, silica andalumina in the ashes of the fuel that the nal composition of the slag inlime, silica and alumina is represented by a point of the ternarydiagram showing the temperatures of fusion of the various possiblecompositions of SiO2, A1203 and CaO, which point is situated in theeutectic valley comprised between the combinations SOZ, CaO and 2Si02,A1203, CaO, in a section of said eutectic valley defined by the two 1300C. isotherms whereby the slag has a great fluidity.

2. In a dry metallurgical process for the extraction of lead from itsore; the step according to claim 1, wherein the lead is present in asulphide ore, `and is extracted by the reaction thereof on metalliciron, with the separation of the metal from the slag being enhanced bythe simultaneous dissociation of the eutectic of mixed sulphide formedduring the process.

3. In a dry metallurgical process for the extraction of lead fromy itsore; the step according to claim 1, wherein the lead is present in asulphide ore, and is extracted by the reaction thereof on metallic iron,with the separation of the metal from the slag being enhanced by theiuidity of the eutectic slag.

4. In a dry metallurgical process for the extraction of lead from itsore; the step according to claim 1, wherein the lead is present ingalena and is extracted from the latter by the reaction thereof onmetallic iron.

5. In a dry metallurgical process for the extraction of lead from itsore; the step according to claim l; wherein the lead is present in anoxidized ore reduced by means of carbon, with the separation of theliberated lead from the slag being enhanced by the uidity of theeutectic slag.

References Cited in the file of this patent Handbook of NonferrousMetallurgy, II, Recovery of the Metals, Liddell, second ed., 1945, pp.159, 160, 162.

1. IN A DRY METALLURGICAL PROCESS FOR THE EXTRACTION OF LEAD FROM ITSORE, THE STEP OF ADJUSTING THE COMPOSITION OF THE SLAG FORMED AT THE ENDOF THE PROCESS BY ADDING TO THE ORE AND FUEL A COMPOUND OF LIME, SILICAAND ALUMINA THE PROPORTIONS OF WHICH ARE SO RELATED WITH RESPECT TO THEINITIAL CONTENT OF THE ORE GANGUE AND OF THE CONTENT OF LIME, SILICA ANDALUMINA IN THE ASHES OF THE FUEL THAT THE FINAL COMPOSITION OF THE SLAGIN LIME, SILICA